Autism is a disorder defined by altered engagement with the social world that emerges at early stages ofthe disorder. Thus, increase knowledge on the critical periods of typical development during which these early social skills emerge and mature and on the underlying neurobiological systems that underlie these skills will give unprecedented opportunity to further understand the neurobiological source of the early diagnosis markers of autism. Although research examining the precursors of human social abilities during early infancy has significantly increased in the last few years, critical information on the neural substrates that support these early developing social skills is still lacking. One ofthe main reasons being the limitations in neuroimaging the human brain in infancy, and to study brain-behavior relationship across development using longitudinal studies. Thus, knowledge in this domain must emerge from translational research examining both human populations and animal models. Rhesus monkeys provide a remarkable opportunity in this domain given (1) the rich and complex social structure in which they develop and navigate, (2) the progressive development of the basic social skills required to develop normal social relationships, and (3) the similarity with humans in brain and cognitive functions development. Thus, Aim 1 will follow longitudinally the development of social visual engagement processes, including attention to, detection and integration of social signals in normally developing rhesus monkeys from birth to 6 months, using neuropsychological marker tasks similar to those employed in the typical and atypical human population (Project I) to facilitate cross-species comparisons. This will allow defining significant critical periods during which these processes emerge and refine. Aim 2 will investigate in the same animals the maturational changes in brain networks mediating these basic social processes using noninvasive neuroimaging procedures. These studies on the normally developing rhesus monkeys will provide unparalleled information and a critical non-human primate model that could be used for further investigations targeting gene-behavior relationships and therapeutic interventions.